Project Summary/Abstract Drugs of abuse are known to cause long-term changes in the synaptic plasticity of reward circuitry and, ultimately, persistent changes in behavior. Understanding the mechanisms underlying these changes is a key open question. As the reward circuitry and the learning and memory circuitry share key nodal points, new discoveries in the learning and memory field will have the potential to shed light on aspects of drug-seeking behavior. In particular, it is well established that gene expression is required for long-lasting forms of synaptic plasticity and long-term memory formation. Very recently, studies demonstrated that epigenetic regulation of gene expression during memory consolidation can modulate gene expression dynamics, resulting in surprising effects on memory formation. For example, inhibition or deletion of histone deacetylase 3 (HDAC3) in the nucleus accumbens leads to maintained expression of Nr4a2 (nuclear orphan receptor 2), correlating with cocaine- context associated memory formation. Nr4a2 is a transcription factor for tyrosine hydroxylase and the dopamine transporter, defining enzymes of dopaminergic signaling. The medial habenula (MHb), a region that highly expresses both HDAC3 and NR4A2, and its projections have recently been identified as main targets of drugs of abuse. I have already demonstrated that the MHb is engaged by cocaine-primed reinstatement of CPP and activation of the MHb induces a reinstatetement-like phenotype (Specific Aim 1). The F99 phase of this proposal will test whether Nr4a2 within the MHb is a key regulator of cocaine-primed reinstatement (Specific Aim 2.1). It will test whether epigenetic alterations induced by drugs of abuse lead to misregulation of Nr4a2 within the MHb (Specific Aim 2.2). Lastly, using a ChIP-seq approach, it will seek to identify alterations in Nr4a2 function that engage the reinstatement of drug-associated behavior (Specific Aim 2.2). The proposed project will also help the candidate, Mr. Alberto Lpez, achieve his career goal of becoming an independent investigator at a research-focused institution. This project provides training in cutting-edge research skill, including FACS, ChIP-qPCR, and viral vectors to manipulate gene expression. Further, the proposed studies will provide professional and technical training to prepare the candidate to successfully transition to a postdoctoral position (K00) in a laboratory that studies the neural-circuitry driving drug-seeking behavior. The University of California, Irvine is an ideal environment for training towards achieving these goals. UCI is a university with 1) an intellectual environment that encourages cooperation and collaboration, 2) technical resources to perform cutting-edge research, and 3) renowned faculty that encourage pedagogical training, mentorship, and development of other necessary professional skills. The complete plan proposed here for both the F99 and K00 phases has been designed to develop an independent neurobiologist prepared for a transition to a successful postdoctoral position and, ultimately, independent tenured investigator.